From WO 03/030329 A1 a method of operating a wind farm which is connected to an electric power network is known. In this method, a correlation between wind speed and output capacity of the wind farm is input into a data processing unit. This correlation controls the output capacity of the wind farm based upon the wind in such a way that at high wind speeds, the wind farm can provide only a limited output, to prevent damage to the individual wind turbine generator systems. The disadvantage of the described wind farm is that the control process is relatively complicated because the output control, which is dependent upon wind speed, leads rapidly to control instabilities, and the output capacity is determined by wind speed.